Pion, pion-pion, and pion-nucleus interactions

This survey is devoted to describing the early studies of I.I. Gurevich on pion physics that were performed by the photoemulsion method and the studies of the pion-pion interaction that were made by his colleagues on the basis of the hydrogen-bubble-chamber and the magnetic-spectrometer method (as well as on the basis of the photoemulsion method). Two approaches—an extrapolation of experimental data from the physical region to the pion pole and a theoretical calculation based on the Roy integral equations—are used to deduce information about the pion-pion interaction. The first results obtained for pion-pion and pion-nucleus interactions in the experiments that are being currently performed in Brookhaven and at CERN ( ππ interaction) and at TRIUMF (Canada) and in Brookhaven (pion-nucleus interaction) are presented, along with the existing theoretical concepts in these realms of physics.